ΠΙ. Central Stars
Spectral Analyses of late-type [WC] Central Stars:
Element Abundances of N, Ne and Si
U. Leuenhagen
Institut für Astronomie und Astrophysik, Universität Kiel, 24098 Kiel, Germany;
(present address: I. Phys. Institut, Universität Köln, Zülpicher Str. 77, D - 5 0 9 3 7 Köln, Germany)
The optical spectra of [WC] central stars of the latest subtypes ([WC11], [WC12]) exhibit
not only stellar emission lines of hydrogen (in some cases), helium, carbon and oxygen, but
also features of nitrogen (Ν II, Ν m), neon (Ne I), magnesium (Mg II), aluminium (Al ill),
silicon (Si III, Si IV) and iron (Fe III). Some of these features are also visible in the peculiar [WC9]-type object SwSt 1 which has a lower final wind velocity and a smaller wind
density than normal [WC9] stars.
Based on model atmospheres accounting for the elements hydrogen, helium, carbon
and oxygen (Leuenhagen et al. 1996, A&A 312,167; Leuenhagen 1997, this proceedings)
first results of the analyses of nitrogen, neon and silicon lines are available. The trace elements are represented by the following model atoms: Ν I - Ν I V (63 NLTE plus 22 LTE
levels), Ne I - Ne II (9 NLTE levels) and Si III - Si ν (32 NLTE levels). The observed nitrogen and silicon lines appear as emission or P-Cygni shaped features, except for IRAS
21282 and V 348 Sgr whose wind densities are very small (—• absorption lines of Ν and
Si). If present, the observed neon lines are P-Cygni shaped, indicating a formation region
far out in the wind.
The element abundances (Table 1) are determined by fitting preferably unblended and
distinct lines. In some cases only upper limits can be given (noisy spectrum or blended
lines). A correlation can be found between the hydrogen and nitrogen abundances. Only
in one of seven objects of the subtype [WC11] or [WC12], namely in CPD-56°8032, hydrogen is definitely absent. In the same object the nitrogen abundance can be restricted to
a very sharp upper limit of 0.1%. Because of the simple model atom the abundances of
neon should be taken as preliminary results.
Table 1: Element abundances (mass fractions) of nitrogen, neon and silicon
in the atmospheres of [WC] central stars of latest subtypes.
subtype
T.
β*
ßsi
[kK]
[%]
[%]
[%]
SwStl
37
[WC9]
<0.5
PM1-188
[WC11]
1
35
CPD-56°8032
32
[WC11]
<0.1
M4-18
[WC11]
31
<0.5
He2-113
[WC11]
30
0.5
K2-16
[WC11]
1
30
IRAS 21282+5050 [WC11]
28
<0.5
V348Sgr
[WC12]
20
0.5... 1
a: no spectra available; b: no neon lines detectable
2...4
2...4
_
_
a
a
_
a
>4
_b
2
1...2
2...3
0.5... 1
0.5... 1
0.5... 1
0.5...1
<0.1
<0.1
119
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available at https:/www.cambridge.org/core/terms. https://doi.org/10.1017/S0074180900130050